Self-sustaining gas tube circuit



April 8, 1952 w. M. WEBSTER, JR I 2,591,899 I SELF-SUSTAINING GAS TUBE CIRCUIT Filed Jan. 2, 1951 INVENTOR WILLIAMMWEBSTERJR ATTORNEY Patented Apr. 8 1952 SELF-SUSTAINING GAS TUBE CIRCUIT William Merle Webster, In, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application January-2, 1951, Serial No. 203,950

9 Claims. (01. 315-349) This invention relates to improvements in systems for operating gas filled electron tube circuits, and particularly to an improved system for operating a gas filled electron tube of the type wherein the functions of ionizing the tube gas and of passing current through the ionized gasare separated.

In a copending application of E. 0. Johnson, Serial No. 185,745, filed September 20, 1950, and assigned to the assignee of the present invention, there is described a gas filled electron tube in which space charge neutralizing ions are generated by an-auxiliary ionizing discharge of electrons between an auxiliary emitter and one or more of the main tube electrodes. With this arrangement, two very important advantages are attained.

First, it is found that very high current can be passed between the main emitter and collector electrodes at potentials far below those required toionize the gas. Second, it is found that the current flow between main emitter and collector can be controlled in various ways, one of which is by means of a control electrode similar to that used in the conventional vacuum tube.

For simplicity, gas tubes of the type just described are referred to herein as separated functio gas tubes.

While the principal current through a separated function gas tube can be sustained with a voltage considerably less than that required to ionize the tube gas, it is still necessary to have a voltage of sufficient amplitude to sustain the auxiliary ionizing discharge.

In a copending application of H. N. Crooks, Serial No. 248,771, filed September 28, 1951 and assigned to the assignee of the present invention, there is disclosed what maybe termed a self-sustaining oscillatory gas tube circuit. In the system disclosed in said Crooks application, a separated function gas'tube is connected in an oscillatory circuit from which 1 stepped-up alternating voltage is derived and rectified to provide a voltage which will sustain an ionizing discharge, so that the primary source of operating voltage can be less than that required to i onize the tube gas. c

It is a principal object of the present invention, to provide an improved self-sustaining circuit for operating a separated function gas tube with a source of voltage less than that required to ionize the tube gas.

A more specific object of the invention is the provision ofan improved and simplified arrangement for initiating the operation of a self-sustaining gas tube circuit,

, site ends of a tank circuit l8 through capacitors, I

Another object of the invention is to provide an improved direct current inverter network. comprising a self-sustaining gas tube circuit.

An ancillary object of the invention is to provide an improved separated function gas tube.

In accordance with the invention, certain of the foregoing objects and advantages are attained by utilizing oscillatory voltage developed by a separated function gas tube circuit prior to ionization of the tube gas. This oscillatory voltage is stepped-up by a transformer sufficiently .toprovide an ionizing voltage for the tube gas. In accordance with a further feature of the invention, this stepped-up alternating voltage may be converted to unidirectional voltage by rectification in the ionization section of the gas tube. A further feature of the invention provides a gas tube structure especially adapted to prevent .backfiring or inverse current flow in a gas tube energized in accordance with the invention. f

7 A more complete understanding of the invention may be had by reference to the following description of illustrative embodiments thereof, when considered in connection with the accompanying drawing, wherein:

Fig. 1- isla schematic diagram of a self-sustaining gas tube oscillator system arranged in accordance with the invention,

Fig. 1a shows the structure of a gas tube such as may be used in the circuit of Fig. 1,

Fig. 2 is a schematic diagram of a direct current inverter network embodying the principles of the invention,

Fig. 2a illustrates the structure of a gas tube especially adapted for use in the circuit of Fig. 2 and embodying certain principles of the invention,

' Fig. 3 is a graph illustrating the operation of the network of Fig. 2, and 1 Fig, 4 is a circuit diagram of a modification ofthe network of Fig; 2 embodyingthe principles of the invention.

Referring to Fig. 1 of the drawing, a circuit embodying the invention includes a gas filled electron tube [0, structural details of which are given hereinafter. The tube I0 is provided with an anode l2 and a main cathode [4, with a control electrode l6 therebetween. The anode l2 and control electrode [6 are connected to oppo- 20 and 22, respectively. The cathode I4 is connected to an intermediate point on the coil 24 .of; the tank circuit l8 to, complete a so-called Hartley oscillator network. The coil 24 also serves as the primary winding of a transformer 25, for a purpose explained hereinafter. A variable capacitor i9 is provided for tuning the tank circuit IS.

A battery 26 is shown to represent a source of voltage less than that required to ionize the tube gas. The battery 26 is connected to the anode l2 and to the cathode it (through tl e coil 26) to energize the oscillator circuit.

The tube It also is provided with an auxiliary cathode 28, cooperable with the anode E2 or the cathode M, or both, to ionize the gas in the tube Is. In order to provide a voltage of sufficient amplitude to ionize the tube gas, the auxiliary cathode 28 is connected through a rectifier 39 to the secondary winding 32 of the transformer 25.

In a somewhat similar system described in the above-mentioned Crooks application, circuit operation is initiated by temporarily connecting the voltage source to the tank coil to obtain in the ionizing circuit an induced voltage of sufficient amplitude to ionize the tube gas. In accordance with the present invention, this switch is eliminated.

Prior to ionization of the tube gas, the main tube electrodes l2, l4 and IE; will cooperate with the tank circuit I8 to develop a small oscillatory voltage across the tank circuit 18. By providing very close coupling between the transformer windings 24, 32, and making the ratio of secondary to primary turns relatively high, this small tank circuit voltage can be stepped-up sufficiently to cause the rectifier 38 to conduct and charge a capacitor 34 connected in series therewith. The capacitor 34 also is connected between the auxiliary cathode 23 and the voltage source 26. As soon as the sum of thecapacitor voltage and the source voltage is large enough to ionize the tube gas, ionizing current will flow from the auxiliary cathode 28 to the main anode I2. Upon ionization of the tube gas, the main cathodeanode current of the tube I!) will increase substantially, causing a corresponding increase in the oscillatory voltage developed across the tank circuit l8. In turn, this oscillatory voltage will be coupled into the ionizing circuit through the transformer 25 to maintain ionization of the tube gas. If desired, the stepped-up voltage developed across the capacitor 34 also can be made available for energizing other circuits which may be connectedto a pair of output terminals 36.

Thus, prior to ionization of the tube gas, the tube Hi can be said to operate as a vacuum tube, generating a small oscillatory voltage in the tank circuit is. As soon as the tube gas becomes ionized, the tube 15 will operate as a separated function gas tube, with the advantages of low voltage grid controlled current flow characteristic of such tubes. 7

Consider, for example, the tube shown in cross section in Fig. 1a. In Fig. 1a, a gas tight envelope I is provided with a cathode M. A U- shaped control electrode 01' grid l6 and a U- shaped anode l2 partially surround the cathode M. The grid 16 comprises a plurality of parallel wires I! which are supported in spaced relation. The anode [2 may be a sheet metal element.

In order for the tube ii) to have sufficient amplification to start oscillation before ionization of the tube gas, it is deemed preferable to modify the grid and anode structures slightly. A mesha type grid section lfia may be provided at a point relatively close to" the cathode it, while an anode extension I2a may be brought close to the grid section Ilia. These closely spaced elements Ilia, IZa will assist in setting up pre-ionization oscillations.

Opposite the open ends of the grid i6 and the anode l2 there is mounted a cylindrical focusing electrode 23 provided with an elongated slot 21 facing the open ends of the grid and anode structures. An auxiliary cathode 28 is mounted coaxially within the focusing electrode 23.

A tube having a structure such as that shown in Fig. 2 can be operated as follows:

If a voltage greater than that required to ionize the gas in the tube is applied between the auxiliary cathode 28 and the anode [2, a current will flow which will ionize the gas in the tube.

As a result, a highly conductive mixture or plasma of ions and electrons will be created within the tube envelope. The focusing electrode 23 is effective to concentrate the ionizing current, making it possible to obtain high plasma densities with very small amounts of current or power. With the tube gas ionized to create plasma in the manner just described, it becomes possible to pass a relatively high current between the main cathode and the main anode with a voltage drop which may be of the order of 0.1 volt or less. Furthermore, it becomes possible to control this main cathode-anode current by means of a control electrode disposed in the space path as shown. In some instances, the focusing electrode is utilized to control the ionizing current in order to control the main tube current. Otherwise, the focusing electrode may be connected directly to the auxiliary cathode 28, as in Fig. 1.

In accordance with a further feature of the presentinvention, the rectifier 30 of Fig. 1 can be eliminated Without adversely aifecting system operation, and in such manner that the system stillwill function as a direct current inverter, furnishing stepped-up unidirectional output voltage from a low voltage source. A system illustrating this feature of the invention is shown in Fig. 2.

In the system shown in Fig. 2, a gas tube Illa is provided which is substantially the same as the tube Hi of Fig. 1. The tube lea, however, preferably has one additional electrode; namely, an auxiliary control electrode 29 in the space between the auxiliary cathode 28 and the main electrodes l2, 14, I6. The purpose of the auxiliary control electrode 29 will be explained hereinafter. The structure thereof may be as shown in Fig. 2a, comprising a plurality of parallel wires supported. in spaced relation adjacent the slot 2'! in the focusing electrode 23.

The remainder of the circuit of Fig. 2 also corresponds substantially with the circuit of Fig. l, with the exception that the rectifier 3-9 of Fig. 1 is eliminated in the circuit of Fig. 2.

In a copending application of I. Wolff, Serial No. 212,632, filed February 24, 1951, and assigned to the assignee of the present invention, there is described a self-sustaining oscillator system embodying a separated function gas tube, in which a pulse voltage is utilized to support the aux- Fig. 2. The dot-dash line B represents the voltage at the anode l2, being separated from the reference line A by a distance Eb which represents the voltage of the battery 25. The broken line C represents the voltage level to which the auxiliary cathode 28 must be driven to ionize the tube gas. Thus, the line C is separated from the line B by a distance E1, representing the ionization potential of the tube gas. A line D represents the D. C. voltage at the upper output terminal 36a, and is separated from the reference line A by an increasing distance E0, representing the output voltage available between the terminals 36a, 36b. An undulating line F represents the alternating voltage at the auxiliary cathode ,28, as induced in the secondary winding 32.

Prior to ionization of the gas in the tube Illa, a relatively small oscillatory voltage will be developed in the tank circuit l8, as in the circuit of Fig. 1. This voltage will be coupled'into the secondary winding in amplified form. Eventually, as at point F1 in the chart of Fig. 3, the sum of induced voltage and the battery voltage will be sufficient to cause anionizing current pulse to flow from the auxiliary cathode 28 to the anode I2. This current pulse will charge the capacitor 34 by a small amount, raising the level of the line D about which the auxiliary cathode volt age is fluctuating. Ionization of the tube gas will permit an increase in the main tube current, as previously described.

As is explained in the above-mentioned Wolff application, if voltage pulses of relatively high amplitude and repetition rate are applied to the ionizing'electrodes of a separated function gas tube, the main tube current will be substantially independent of the ionizing current.

I Thus, the oscillations in the tank circuit IS in Fig. 2 gradually will build up, providing increasing amplitude pulses of ionizing voltage until the circuit becomes stabilized in full oscillation. It will, of course, be understood that the chart of Fig. 3 gives a simplified picture of the circuit operation, and is given solely as an aid in explaining circuit operation.

Since the line A in Fig. 3 represents the D. C. voltage at the output terminal 36b, the same line also substantially represents the D. C. voltage at the main cathode M. It can be seen from Fig. 3 that the auxiliary cathode voltage will be rather highly positive with respect to the main cathode l4 during each positive half cycle of the auxiliary cathode voltage. Consequently, it is possible that inverse current might flow from the main cathode I 4 to the auxiliary cathode 28 during these positive half cycles of auxiliary cathode voltage. Such inverse current fiow would, of course, be in a direction such as to discharge the capacitor 34, thereby interfering with .the desired circuit operation. To prevent this possible inverse current flow or backfiiring, the

auxiliary control electrode 28 is connected to the a applied to the auxiliary cathode 28 and to the auxiliary control electrode 29, the control elec- Fig. 4.

In accordance with a further embodiment of the invention, the possibility of inverse current flow can be avoided by making the auxiliary ionizing electrode an electron collector or anode rather than an electron emitter or cathode. This arrangement is illustrated in the circuit of In Fig. 4, a separated function gas tube I01) has no auxiliary control electrode, but is provided with an auxiliary anode 28a rather than with an auxiliary cathode as in the circuit of Fig. 2. Otherwise, the circuit of Fig. 4 is identical with that of Fig. 2.

In operation of the system of Fig. 4, ionizing current will flow from the main cathode M to the auxiliary anode 28a during those intervals when the alternating voltage induced in the secondary winding makes the auxiliary anode 28a "sufiiciently positive with respect to the cathode I 4. During the alternate half cycles of voltage across the secondary winding 32, there will be little likelihood of drawing electrons from the auxiliary anode.

It can be seen that the present invention provides a simple and efi'icient system for operating a separated function gas tube from a source of voltage less than that required to ionize the tube gas.

What is claimed is:

1. In a system for operating a gas filled electron tube of the type having electrodes including an anode, a cathode, a control electrode therebetween, and an auxiliary electrode cooperable with one of said electrodes for passing ionizing current through the tube gas, in combination, an oscillatory circuit connecting said anode, said cathode and said control electrode and including a first coil, a source of voltage less than that required to ionize said tube gas, said voltage source being connected between said anode and said cathode to sustain low amplitude oscillations in said oscillatory circuit prior to ionization of said tube gas, and means connecting said auxiliary electrode to said one electrode through said voltage source to derive from said low amplitude oscillations a voltage of suffioient amplitude, when added to said source voltage, to ionize said tube gas, said means comprising a second coil having a relatively large number of turns as compared to said first coil and closely inductively coupled to said first coil.

2. A system as defined in claim 1 wherein said auxiliary electrode comprises an anode electrode.

3. A system as defined in claim 1 wherein said auxiliary electrode comprises a cathode electrode.

4. A system as defined in claim 1 wherein said gas tube further includes a control electrode between said auxiliary electrode and said another electrode, and connections from said coils to said auxiliary electrodes to supply out-of-phase voltages to said auxiliary electrodes from said coils.

5. In a system for operating a gas filled electron tube of the type having electrodes including an anode, a cathode, a control electrode therebetween, and an auxiliary electrode cooperable with one of said electrodes for passing. ionizing current through the tube gas, in combination, an oscillatory circuit connecting said anode, said cathode and said control electrode and'includin a first coil, a source of voltage less than that required to ionize said tube gas, said voltage source being connected between said anode and said cathode to sustain oscillations in said oscillatory circuit, a second coil coupled inductively to said first coil and having a greater number of turns than said first coil to induce across said second coil an alternating voltage substantially greater than said oscillatory voltage, a capacitor, and a series circuit consisting of said voltage source, said capacitor and said second coil connected between said auxiliary electrode and said one electrode to provide between said last named two electrodes a pulsating voltage of amplitude sufficient to sustain ionization of said tube gas and to provide across said capacitor a unidirectional voltage of amplitude greater than said source voltage.

6. A system as defined in claim wherein said auxiliary electrode comprises an anode electrode.

7. A system as defined in claim 5 wherein said auxiliary electrode comprises a cathode electrode.

8. A gas filled electron tube having electrodes including an anode, a cathode, a control electrode therebetween, an auxiliary cathode cooperable with one of said electrodes for passing ionizing current through the tube gas, and a control electrode between said auxiliary electrode and said one electrode.

9. In a system for operating a gas filled electrontube of the type having a plurality of electrodes including a first pair of electrodes cooperable to pass ionizing current through the gas in said tube, a control electrode between said pair of electrodes to control said ionizing current, a pair of electrodes cooperable to pass current through the ionized'gas, and a second control electrode between said last named electrode pair for controlling said last named current, in combination, a source of voltage less than that required to ionize said tube gas, an oscillatory circuit, connections between said oscillatory circuit, said last named electrode pair, said control electrode, and said-voltage source for sustaining oscillations in said circuit upon ionization of said tube gas, means coupling said oscillatory circuit to said first named electrode pair to provide a voltage between said first named electrode pair sufiicient to ionize said tube gas, and a capacitor connected between said first named electrode pair to be charged by said ionizing current fiow.

\VILLIAM MERLE WEBSTER, JR.

REFERENCES crrEn UNITED STATES PATENTS Name Date Meier Sept. 13, 1938 Number 

